1. Field of the Invention
The invention relates generally to synchro devices and particularly to synchro resolver devices in a flight instrumentation situs where the output signals of a synchro resolver normally require demodulation.
2. Description of the Prior Art
Synchro devices such as synchro resolvers are utilized in numerous flight instrument applications, as well as in applications in many other fields, for providing a measure of angular position. For example, synchro resolvers are utilized to provide an angular position feedback signal in closed loop positioning servoes. In such an application, the resolver rotor may be coupled to the element being positioned by the servo and a sinusoidal voltage, typically having a frequency of 400 Hz, applied, for example, to the resolver rotor windings. The sinusoidal excitation voltage is coupled from the rotor windings to the stator output windings to provide sinusoidal output signals having respective amplitudes proportional to the sine and cosine of the angle at which the rotor is positioned. The output voltages are either in-phase or out-or-phase with the excitation voltage depending upon the angular position of the resolver rotor. It is well known in the art that the output voltages may be converted to d.c. signals of amplitude proportional to the respective sine and cosine values and of polarity in accordance with whether the output voltage is in-phase or out-of-phase with the excitation signal.
Conventionally, bulky, complex and expensive synchronous demodulators have been utilized to convert the sinusoidal synchro output voltages to corresponding d.c. levels. U.S. Pat. No. 4,270,077, issued May 26, 1981, assigned to the Applicants' assignee, however, discloses a demodulatorless synchro resolver angular position sensor which provides the sine and cosine of angular position by applying a continuous square wave excitation to the resolver rotor winding. The corresponding square wave outputs of the sine and cosine windings of the resolver stator are sampled in time synchronism with the excitation at a predetermined time phase of the square wave excitation cycle. The sampled sine and cosine amplitudes are converted into digital format via an analog-to-digital converter for application to a digital processor. The upper corners of the positively-going leading edges and the lower corners of the negatively-going leading edges of the continuous square wave excitation waveform are rounded to minimize ringing of the sine and cosine square wave outputs from the resolver.
The above described apparatus, utilizing continuous square wave excitation and time phase sampling thereof, may often be disposed in a flight instrument situs where reduced size, cost, and power dissipation are highly desirable objectives. The amount of circuitry, necessary to effect the continuous square wave excitation technique associated with the above described apparatus, however, is not always consistent with these desired objectives. Therefore, there is a need for a simpler and less expensive apparatus for converting resolver sine and cosine output voltages into a digital format.